DE2500083A1 - ALUMINUM WICKED ALLOYS AND PROCESSING METHODS - Google Patents

Description

UR. ING. F. WUKSTHOKF 8 MUNICH OO UR. K. τ. PKOlIM AN X "*" WKIOKHHTHAtISK 8 DR. ING. I>. BKHRKNS «« ro * (081 »

TKLBX S 34 070 UIPL. ING. R. GOETX

TKLKOMAMMEl PATENTANWÄLTE PKOTKCTPiT (KT

2500083 _1A . _{45 855}

Description of the patent application

Societe de Vente de 1 »ALUMINUM PECHINEY 23 bis, rue Balzac - 75008 Paris, France

concerning

Wrought aluminum alloys and methods of processing

The invention relates to products made from wrought aluminum alloys with a very low hydrogen content and an isotropic structure equiaxed grain, which has practically the same mechanical properties in all directions and a particularly low critical quenching rate · The products or wrought alloys are obtained by a heat treatment at a temperature little above the solidus curve · you allow a noticeable weight saving in components, especially in aircraft construction, as well as hardening in boiling water or even air hardening without noticeably impairing the mechanical properties

In industry and especially in aircraft construction, increasing amounts of wrought aluminum alloys are being used to an increasing extent (which are processed by rolling, forging, die forging, extrusion or otherwise) · So are commonly certain components of the cells or wings, which are subjected to high mechanical loads, made of sheet metal with a Initial thickness made up to 90 or 100 mm and sometimes more.

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It is also known that these aluminum products? Wrought alloys are almost always anisotropic and have a flow texture (fiberage) caused by forming.

to

The mechanical properties across the flow lines are mechanical Properties in the longitudinal direction or parallel to the main direction of deformation are significantly worse.

(Stripes) The main disadvantage of the "flow texture" or lines and the associated anisotropy is that one takes into account the decrease or weakening of the properties in the transverse direction must provide; therefore, in numerous cases, noticeably higher workpiece weights are required with the known, annoying ones Disadvantages on the maximum payload of the aircraft.

The invention was based on the object of finding wrought aluminum alloys which do not have these disadvantages.

The task is accomplished with the help of the semifinished product according to the invention Wrought aluminum alloys, which are characterized in that they have a practically homogeneous and isotropic structure or microstructure and that they have practically the same mechanical properties in all directions (yield point, breaking strength, elongation, The progression of cracking). The invention relates in particular to products made from wrought aluminum alloys Specifications "A-ZG", "A-ZGU" or "A-U" according to AFNOR A-02.001 and A-02.002 or "7000" and "2 000" according to American Aluminum Association standards.

The invention also relates to a new heat treatment method of products obtained by conventional kneading methods in order to reduce the anisotropy of the mechanical properties or even to switch it off completely »

It was also surprisingly found that this new heat treatment processes for these alloys are unexpected The effect is a considerable reduction in the critical speed of deterrence

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the rate of cooling of an alloy during quenching equilateral from the dimensions of the workpiece and the type and temperature of the nutty hardening medium. The cooling rate is known to be sufficiently high must in order to prevent dissolved alloy components from precipitating again

A critical quenching rate is defined for each type of alloy, for example about 40 degrees / s for alloys AZ5GÜ (KF A 02.001) or 7075 (according to A.A.). For lesser ones Cooling speeds, the mechanical properties of the alloy (Vickers hardness, breaking strength) decrease rapidly, while for higher speeds these properties remain practically constant or increase only very slightly.

The combination of these two effects - turning off the Anisotropy and reduction of the critical quenching speed - allows a more efficient processing of the workpieces and use of the components, because they have practically identical mechanical properties in all directions, and that massive workpieces can be quenched in less energetic media than cold water (for example in boiling water Water or even in pulsating air), which means the risk of quenching cracks and the need for artificial aging are eliminated.

The new heat treatment process according to the invention is based on the surprising results of a study on so-called "burning" / = eutectic melting).

In current practice, the heat treatments of aluminum alloys are carried out at a temperature which is one Do not exceed certain so-called "combustion" temperatures above which, in the worst case, a complete breakdown other falling of the workpiece during chamfering is observed and

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which in all cases leads to a decrease in mechanical properties leads. A "burned" structure is characterized by the presence of irreversible porosity as well of liquid phases,

It has now been found that, contrary to current practice, a workpiece made of aluminum alloy _{can be brought above the solidus temperature T 1} but below the liquidus temperature T ₂ - without being damaged as a result - provided that the workpieces at this time ^ 0.5 ppm, preferably ^ - 0.2 ppm and even ^ 0.1 ppm, hydrogen is contained, which can escape _{up to the temperature T 2.} For this purpose, degassing is carried out in the usual way and a renewed uptake of hydrogen before and during the treatment is prevented or hydrogen is fixed in a constant form.

In this way, a “flowing texture ¹¹ can be virtually completely eliminated.

By choosing the appropriate treatment _{temperature T ^ (T 1} <T ^ < T ₂ ) and the duration of the treatment at this temperature for each type of alloy, all intermediate states between a fibrous flow structure and a recrystallized structure with equiaxed grain can be obtained.

This treatment is particularly effective on alloys that have secondary phases of elements such as hangan, chromium, zirconium and / or contain iron, which is known to be the

Considerably inhibit recrystallization if they precipitate very finely.

The new treatment, in which the alloy is partially returned to the liquid phase, promotes crystal growth of the secondary phases and allows recrystallization without preventing the hardening that occurs on the dispersion of the secondary phases is based. The appearance and dimensions of the

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Accumulated precipitates are characteristic of the treatment, as explained below and shown in the photomicrographs.Ba in addition, these congealed precipitates serve as nuclei for the precipitation of coarse phases such as XMgZn ₂ during quenching, it is understandable that this number of conglomerated precipitates decreases to the extent , in which its dimension increases, the hardenability of the alloy is improved and the critical quenching rate drops significantly below the usual values, as shown in Examples 3 and 4 below.

The alloys of the specification A-U4SG (Cu 4.4>, Si 0.9 fi, Mg 0.5 *, Mn 0.6 *), 7075 ( Zn 5.6 #, Mg 2.5 #, Cu 1.5 #, Cr 0.30 £, Mn <0.3 #) or according to the French regulations A-Z5GtJ as well as even more powerful alloys such as A-Z6G2U2 or A- Z9G3U (7001 after Α · Α ·).

The treatment according to the invention is followed by a solution heat treatment at a temperature <T ₁ in order to dissolve the heterogeneous areas that have formed between T ₁ and T ₂ «

In the following examples: LE s yield strength (in hectobar hb); R = breaking strength

(in hectobar hb); A = elongation at break (£) and K _{1 (J} = (toughness).

example 1

The following properties were determined on a 40 mm sheet made of the aluminum alloy 7075 (ASTM), specifically in condition 16 (ie 3 h solution heat treatment at 47O ⁰ C, quenched with cold water and aging for 24 h at 120 ⁰ C):

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Determination in: LE R. A. ^K lc hh hb % Longitudinal direction 52.4 59.1 14.4 127 Thickness direction 52.7 56.8 3.3 68

The same sheet, solidus temperature T _{1 is} approximately 535 ⁰ C, was 1.5 hours at 54O ⁰ C (5 ° <T ₁₎ and then for 3 hours at 47o ⁰ C (65 ⁰ C <· T ₁₎ is held, with Quenched in cold water and aged at 12O ⁰ C for 24 h:

Determination in: LE R. 3 A. O * lc hb hb 4th % O Longitudinal direction 52.0 57, 16, 108 Thickness direction 52.4 57, 17, 88

The critical value K _{1 (J} for the toughness is given in hbj / mm · It was found that a practically perfect isotropy of the mechanical properties was obtained and that the aaisotropy of the toughness was considerably reduced; the toughness in the thickness direction was about 30 # gone up·

Example 2

A 50 mm sheet of the aluminum alloy A-U4SG was examined (Cu 4.3 #, Si 0.85 $, Mg 0.45 $>, Mn 0.58 #, Pe 0.18 f>, T ₁ about 525 ⁰ C). after hot rolling and a customary treatment for condition T6 (solution heat treatment for 8 h at 505 ^° C.).

Determined in: LE R. A. hb hb Jt L (longitudinal = rolling direction) 46.0 51.1 12.0 B (width) 43.5 49.0 9.0 D (thickness) 41.8 47.5 5.2

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The same sheet was subjected to a heat treatment according to the invention:

4 h at 535 ⁰ C (1O ⁰ C <T ₁ )

-3 h solution annealing at 505 ⁰ C (2O ⁰ C < T ₁ )

Quenching with cold water

8 h aging at 175 ^° C

determination in: LE 9 R. , 2 A. 3 hb O hb , 5 * 5 I (longitudinal = Rolling direction) 45. 1 50 , 0 9, 0 B (width) 46. 50 7, D (thickness) 46, 51 6,

It was found that the yield strength and the breaking strength were practically the same in all three directions and that the properties in the thickness direction up to the highest values determined for the sheet metal treated in the usual way have gained weight

The micrographic examination of the workpieces according to the invention shows a characteristic recrystallized structure of fine equiaxed grain with numerous precipitations of secondary phases with a diameter> 0.5 Ana, while in the conventionally treated workpieces with a flow structure these (secondary) phases are much more finely diapered and one have mean diameters of 0.05 to 0.1 nm «(It is important to specify that the" mean diameter ¹¹ "or" mean circumference "of these precipitates corresponds to the average size of the coarser particles, which is about 70 to 80 Jt of the volume fraction of the Secondary phases

from

Fig. 1a. 2a and 3a show photomicrographs with fluoroboron reagent (acid) etched samples (composition: fluoroboric acid HBF ^ 1.8 wt .- #, H ₂ O 98.2 50

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Pur the Pig, 1b and 3b were the samples before microscopic Examination treated with Keller reagent ^.

The Pig. 1c and 3c show electron microscope images (in transmitted light).

The microphotographs 1a, 1b, 1c show the structure of a workpiece made of the alloy 7075, which was treated in the usual way for 3 hours at 47O ⁰ C, and the microphotographs 2 and 3 the structure of the workpiece treated _{according to the invention j (1 + ^ T 1} ) . T ₁ = 535 ^° C

Pig. (streaky)

In la you can see the fibrous structure and the secondary phases (Cr, Pe), which are very finely separated in the grain. They are invisible in the optical microscope (1d) and only under the The electron microscope can be seen (1c).

Brief treatment> T ^ (1h at 54O ⁰ C) partially disappears the fibrous rolling texture (2a); the recrystallization takes place in the zones or areas in which the precipitates of the secondary phases Cr and Pe have converged to form a dispersion of spheres that are now visible in the (optical) microscope.

With a longer treatment at T. (4h at 54O ⁰ C and then for 3 hours at 47o C ^0), the rolling texture disappears completely (3a) and the Sekundärpbasen are clearly visible under an optical microscope (3b).

How far the rolling texture is canceled depends on the time at ^ "T ₁ and the distance between T. and T _1. The structure obtained is characteristic of the treatment Structure of a recrystallized alloy after tempering, where the secondary phases are very fine and homogeneous in the grain.

♦ Composition (weight): HNO ^ - 3 %, HCl 2 %, _Q HF 1%, remainder H ₂ O * ~ ^y "

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You reduce the critical quenching speed with The method according to the invention is explained in the following examples and figures.

4 and 5 show in a diagram the dependence of the Vickers hardness of the alloy 7075 (HV10 in kg / mm) on the Quenching speed (V in ° C / s) for a normal Wise treated alloy 7075 (curve A) and an alloy treated according to the invention (curve A) and one according to the invention treated alloy (curve B) · The critical quenching rate is around 40 ° C / s and according to the invention at about 10 ° C / s

They sample shown in Fig. 4 was 24 h at 12O ⁰ C (T6) and which have been swapped in Fig. 5 for 5 h at 105 ⁰ C and then 24 h at 158 ⁰ C (T73) ·

The T73 was found to be a greater increase in hardness (of about 20 kg / mm) than T6 same quenching speed

6 and 7 show the dependence of the Vickers hardness of alloy 7050 (AZ6GU with 0.10 # Zr) on the quenching rate (in ° C./s), namely with the usual treatment (curves A) and with the treatment according to the invention ( curves B) · to swap the samples for Fig. 6 was 24 h at 12O ⁰ C (T6) and Fig. 4 for 24 h at 12O ⁰ C and then 24 h at 163 ⁰ C (T73).

There is also improvement with the treatment according to the invention very big here. For example, forged workpieces made of alloy 7050 can be naturally cooled in subject to still air (cooling rate 0.5 ° C / s) without affecting the mechanical properties with respect to quenching Water noticeably deteriorate; at the same time, all disadvantages of quenching with water are avoided (quenching cracks, Artificial aging)

By reducing the critical quenching speed there are other important additional options, especially:

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1) Higher material thicknesses with the same mechanical properties in the core;

2) less energetic deterrent media (cold water), for example boiling water, as well as reducing the residual stresses during quenching without the need for stress-relieving annealing,

Example 3

It was the ticker hardness determined at 7075 and for comparison in a conventional manner treated (3 hours at 470 ⁰ C, quenched with water and outsourced = T6) and according to the invention (4 h at 540 ⁰ C, thereafter 3 hours at 47o ⁰ C , quenched with water, water temperature 20 ⁰ C and 100 ⁰ C, outsourced = T6) _#

water

Comparison (T6)

2O ⁰ C 185 100 ⁰ C 123 Hardness decrease 62 = 20 ⁰ C 190 100 ⁰ C 184 Hardness decrease 6 ^.

according to the invention (T6)

100 ⁰ C 184

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Example 4

The mechanical properties of test specimens from a 50 mm sheet metal alloy 7075 were determined in the direction of thickness, namely Nfie usual solution heat treatment for 2 h at 47O ⁰ C, quenching with cold water 2O ⁰ C or boiling water, then rolling by 2 # and aging for 24 h at 12O ° C (T651) and 8 h at 105 ⁰ C and then 24 h at 158 ⁰ C (T351) and b according to the invention) solution heat treatment for 4 hours at 54O ⁰ C and then 2 of the eutectics h at 47o ⁰ C (melt temperature 478 ⁰ C. , solidus temperature in equilibrium 532 ⁰ C), quenching with cold water 20 ⁰ C or "boiling water, rolling by 2% and aging for 24 hours at 12O ⁰ C (T65I) or 8 h at 105 ⁰ C and then 24 h at 165 ⁰ C (T7351)

The following properties were determined in the thickness direction:

water

T651

T7351

comparison

20 ⁰ C

100 ⁰ C

according to the invention 20 C

100 ⁰ C

R. 54.8 48.2 hb LE 47.5 40.1 hb Α3ί 4 Ji 5 5 i R. 47.1 40.4 hb LE 38.5 30.5 hb AJi 5.2 3.5 * R. 56.7 50.9 hb LE 48.4 42.4 hb AJi 8.7 6.2 Ji R. 55.5 48.3 hb LE 47.6 41.5 hb A * 6.5 6.1 *

12-

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In comparison, quenching with boiling water reduces the mechanical properties by 10 to 20 %, but with the treatment according to the invention by hardly 2%.

The decrease in the critical quench rate is (Pig ·, 4 to 7) accompanied by a much slower decrease the hardness (and correlatively the other mechanical properties) if this speed is below the critical speed In the extreme case, you can put a deterrent in the air (about 1 ° C / s in pulsating air or about 0.5 ° C / s in still air), without noticeable deterioration in mechanical properties,

Example 5

There were determined the mechanical properties of the alloy 7075 in the thickness direction, namely, as usual, and according to the invention treated with quenching in still air and outsource 24 h at 12O ⁰ C.

R LE A

hb hb %

Comparison 34.2 21.2 7.2

according to the invention

(4h / 54O ° C) 48.5 43.0 2.4

Claims

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Claims (2)

STÖ'0083 Claims 1 · Semi-finished products made of wrought aluminum alloys containing copper, magnesium, silicon, zinc and additives that form secondary phases ₍ or impurities such as manganese, chromium, zirconium and iron, in particular the alloys "A-ZG" or ¹¹ AU ¹¹ according to APNOR A-02.001 and A .02-002 or "7000" or "2,000" according to ASTM, characterized by a content <0.5 ppm, preferably <P.2 ppm and in particular £ 0.1 ppm hydrogen, practically identical mechanical properties in all directions and by an isotropic structure with an equiaxed grain, in which the separated secondary phases are present to a considerable extent as aggregates with a diameter> 0.5 / µm « 2. Semi-finished product according to claim 1, characterized in that that in the structure, in addition to equiaxed grain, secondary phase precipitates> 0.5 / µm are still fibrous grain from the deformation texture " 3 "Process for the production of the semi-finished product according to claim 1 or 2, characterized in that the intermediate product is 0.5 h up to 12 h at a temperature T ^. above the solidus temperature T ₁ and below the liquidus temperature T «and then solution annealing _{below T 1 ·} 509828/0682 Blank page